For example, a W-CDMA (wideband code division multiple access) system (hereinafter, referred to as a W-CDMA system) which is one aspect of a mobile communication system has an inner loop transmitting power control function of controlling the transmitting power on a transmission side corresponding to received quality of a radio signal on a reception side. For example, a base station (described as a Node-B as the case may be) controls the radio transmitting power of a radio terminal on the basis of the received quality of the radio signal from a radio terminal. By using an SIR (signal to interference ratio) measured value as a criterion of evaluation of the received quality, the base station measures the SIR of the radio terminal and compares this SIR measured value with a SIR target value. A result of comparison is mapped over a downlink physical channel signal as an up transmitting power control (TPC) bit value for controlling the transmitting power of an uplink and is transmitted to the radio terminal. In this manner, the inner loop transmitting power control function for the radio terminal is realized. Incidentally, the uplink indicates a direction from the radio terminal to the base station and the downlink indicates a direction from the base station to the radio terminal.
In the W-CDMA system, spread is performed by using two kinds of codes, that is, a channelization code and a scrambling code as channel identification spread codes for identifying channel by using a spread code. Down channelization codes of discrete channels are allocated to users in a one-to-one correspondence. A set channelization code realizes data transfer and power control for a single user. As to the power control, for example, Japanese National Publication of International Patent Application No. 2004-529530 (International Publication Pamphlet No. WO 2002/065667) discloses a technique of performing the power control at a timing in accordance with each propagation delay by transmitting TPC signals to a plurality of radio terminals over a single channel.
On the other hand, an F-DPCH (fractional dedicated physical channel) has been proposed as a discrete channel incidental to an HSDPA (high speed downlink packet access)/EUL (enhanced uplink) channel in the sixth and subsequent releases of the 3GPP (3rd Generation Partnership Project) standard specification (3GPP R1-031073).
The F-DPCH has an advantage that in the case that there is no data to be transferred over a discrete channel, transmission of a TPC bit becomes possible by transmitting only this F-DPCH, thereby making the power control of the uplink possible. The frame of the F-DPCH includes 15 slots. The position of the TPC bit in the slot is determined in accordance with a slot format selected from within 10 slot formats. Thus, it sometimes occurs that the feedback time of the radio transmitting power of a radio terminal is made different in accordance with the position of the TPC bit in the slot having the selected slot format.
As described above, in the W-CDMA system when the F-DPCH is applied, the feedback time of the inner loop transmitting power control is determined in accordance with the position of the TPC bit in the slot in the frame format of the F-DPCH.